Volcanoes can be defined as breaks or cracks on the Earth’s surface which allow the flow of hot lava and other substances such as volcanic ash and gasses. These substances find their way to the Earth’s surface through the magma chamber that lies within the volcanoes. Volcanic structures are mainly found in regions where the tectonic plates are diverging or converging. The contents of a volcanic eruption accumulate and solidify to cause the formation of volcanic mountains. One of the most common volcanoes is the ‘cinder cone volcano’ which is symmetrical and shaped like cones.
Check out the UPSC Notes
Volcanoes in the Mid-Atlantic belt
The Mid-Atlantic Ridge (MAR) also known as the Mid-Atlantic Belt, is the range of volcanic mountains that extend from the Arctic (Gakkel Ridge) to the Antarctic (Bouvet Triple Junction) region and stretches up to more than 16,000 kms.
The Mid-Atlantic Ridge, like most of the volcanic structures in the world, is submerged underwater; almost 90% of the volcanic mountain ranges of the Mid-Atlantic Belt are submerged with an approximate depth of 2500 mts.
The range previously covered the two hemispheres and was first discovered in the nineteenth century. However, 90% of the mountain range is submerged underwater; the axial of the Mid-Atlantic Ridge is visible in Iceland.
The Mid-Atlantic Belt is situated at the convergence point of the tectonic plates that form the floor of the Atlantic Ocean. The molten lava from beneath the Earth’s surface spreads at a slow pace on the ocean floor. Hence, the ridge is considered to be “slowly spreading”.
The range spreads across the north-south axis of the Atlantic Ocean. The volcanic mountain range extends from the Arctic Ocean to the southern tip of Africa. The belt extends at mid-lengths on either side of the continent.
The volcanic mountain ranges sometimes reach above sea level forming island groups such as:
- St. Helena
- Tristan da Cunha
- The Azores
Due to the slow-spreading process of the Mid-Atlantic Belt, the Atlantic floor is slowly spreading at the pace of 1-10 cms every year.
Also see: UPSC Preparation Books
Circum Pacific Ring of Fire
The Circum Pacific Ring of Fire is also known by several other terms such as Pacific Ring of Fire, Girdle of Fire, Rim of Fire and the Circum-Pacific belt. The belt extends up to approximately 40,000 kms. and is 500 kms. wide.
The Pacific Ring of Fire is shaped like a “horseshoe.” This region is mainly known for the massive number of volcanic eruptions and earthquakes that occur frequently. The belt lies across the rim of the Pacific Ocean.
The Pacific Ring of Fire spans North America, South America, Kamchatka and some western Pacific islands. The formation of the Pacific belt is a result of the tectonic movement of the tectonic plates below and around the Pacific Ocean.
One of the most interesting facts about the Pacific Ring of Fire is that it is not a single giant mass of volcanic structures. The volcanoes are distributed individually and the explosions and eruptions occur at different times and locations throughout the belt.
Some crucial facts to be noted about the Pacific Ring of Fire are as follows:
- It has been estimated that the Circum-Pacific consists of almost 850-1000 volcanoes that have been active for the past 11,700 years.
- The world’s fourth-largest explosion occurred in the volcanic ranges of the Pacific Ring of Fire.
- More than 350 volcanic structures in the Circum-Pacific belt have been entirely active since historical times.
- However, there are also ranges of inactive volcanoes in the Pacific belt that have been entirely inactive since the past millennium.
- The Pacific belt hosts most of the Earth’s volcanic summits visible above the sea’s surface.
- Ojos del Salado is the world’s highest active volcano in the Circum-Pacific belt.
- Almost 90% of the world’s earthquakes and 81% of the world’s most devastating earthquakes occur in the Pacific Ring of Fire region.
Some of the most famous volcanoes from the Pacific Ring of Fire are as follows:
- Agung (active volcano)
- Sinabung (active volcano)
- Dukono (active volcano)
- Mount Tambora (significant volcanic activity in 1815)
- Mount Pinatubo (major volcanic explosion in 1991)
Also read about How to Prepare for UPSC without Coaching
The intraplate volcanic activities occur within the tectonic plates and they are not related to the divergence or convergence of these plates. The regions that host active volcanoes within the surface of the tectonic plates are commonly known as “hotspots.”
The intraplate volcanoes are mainly formed when the mantle plumes find their way to the Earth’s surface and spread over in the shape of a mushroom. These plume heads generally have a diameter of about 500-1000 kms.
The Hawaiian and Emperor Seamount chains are ideal examples of intraplate volcanoes.
The Circum-Pacific ring of fire and the Mid-Atlantic Belt host the majority of the world’s active volcanoes and almost 90% of the world’s major volcanic activities occur in the region of the Pacific belt. While the world’s most active intraplate volcanoes are found in the Hawaiian and Emperor Seamount Chains, these belts and ridges cover almost all of the world’s distribution of volcanoes along with other volcanic structures.